golang related query

Introduction

With the popularization of the Internet and the increase in data volume, how to efficiently query data has become the focus of many developers. In software development, correlation query is a very common scenario. This article will provide readers with a fast and efficient query method by introducing golang's associated query method.

1. What is a related query?

Associative query refers to a way of querying through the relationship between multiple data tables. In the query, we will compare a certain column of one table with a certain column of another table to get the results that need to be queried. Common relationships include one-to-one, one-to-many, many-to-many, etc.

For example, we have two data tables: employee table and department table. In the employee table and department table, there is a relationship between employees and departments. Each employee belongs to a department, so we can obtain employee information and department information at the same time through the associated query between the employee table and the department table.

2. Related query methods in golang

In golang, we can perform related queries by using ORM tools. This article will use gorm as an example to introduce related queries in golang.

1. One-to-one related query

In golang, one-to-one relationship refers to that in two data tables, each row of data only corresponds to the other A row of data in a table. When using golang to perform one-to-one related queries, we can implement it through physical foreign keys or virtual foreign keys.

(1) Physical foreign key

A physical foreign key refers to the value of a column in one table corresponding to the value of a column in the other table between the two tables that are related. In golang, we can complete one-to-one correlation query by defining a structure. For example, we have two different structures: Employee and Department. The code is as follows:

type Employee struct {
      ID          int
      Name        string
      HireDate    time.Time
      Department  Department
}

type Department struct {
      ID          int
      Name        string
      Description string
}

In the Employee structure, we complete one-to-one related queries by defining the Department structure. This method requires the use of the Joins() method when querying to implement associated queries. For example, we need to query employee information and department information, the code is as follows:

var employee Employee
db.Joins("Department").Find(&employee)

(2) Virtual foreign key

Virtual foreign key refers to the association defined by ourselves in the program as needed. In golang, we can complete a one-to-one correlation query by adding a relationship field and using table A as a related table in table B. For example, we need to query employee information and company information. The code is as follows:

type Employee struct {
      ID          int
      Name        string
      HireDate    time.Time
      CompanyID   int
}

type Company struct {
      ID          int
      Name        string
      Description string
}

var employee Employee
var company Company
db.Model(&employee).Related(&company, "CompanyID")

2. One-to-many association query

The one-to-many relationship refers to the relationship between two data tables , one row of data in one table can correspond to multiple rows of data in another table. In golang, we can complete one-to-many association queries by defining Slice. For example, we have two different structures: Department and Employee. The code is as follows:

type Department struct {
      ID          int
      Name        string
      Description string
      Employees   []Employee
}

type Employee struct {
      ID          int
      Name        string
      HireDate    time.Time
      DepartmentID int
}

var department Department
db.Preload("Employees").Find(&department)

In the Department structure, we complete one-to-many related queries by defining Employees Slice. When querying, we need to use the Preload() method to perform related queries.

3. Many-to-many association query

The many-to-many relationship means that in two data tables, one row of data can correspond to multiple rows of data in multiple tables at the same time. In golang, we can complete many-to-many relational queries by defining arrays. For example, we have two different structures: Product and Category. The code is as follows:

type Product struct {
      ID         int
      Name       string
      Categories []Category `gorm:"many2many:ProductCategories;"`
}

type Category struct {
      ID   int
      Name string
}

var product Product
db.Preload("Categories").Find(&product)

In the Product structure, we complete many-to-many related queries by defining the Categories array. When querying, we need to use the Preload() method to perform related queries.

Conclusion

In this article, we introduced the associated query methods in golang, including one-to-one, one-to-many and many-to-many relationships. By learning the methods in this article, readers can more conveniently perform related queries in golang, and improve query efficiency while efficiently querying data.

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